Metal hydride-based batteries provide a low-cost energy storage system as well as an alternative to Li-ion batteries, which face technical and commercial challenges associated with flammability. Metal hydride batteries operate, in part, via sorption of hydrogen at a negative electrode during charging and desorption of hydrogen at the negative electrode during discharging of the battery. In addition to practical consideration such as cost of materials, important considerations for a metal-hydride battery include the capacity of the negative electrode for storing hydrogen, the thermodynamic and kinetic barriers to storing and releasing the hydrogen, and the stability of the materials, particularly of the negative electrode.
Vanadium-based metal hydride batteries have been proposed, for example by Iwakura et al. (J. Electrochem. Soc., 2000, 147, 2503-2506), due to a theoretical (thermodynamic) maximum of some V-based materials to absorb up to 3.9 mass % of hydrogen, corresponding to a theoretical electrochemical capacity of 1041 mAh/g. In practice, however, V-based metal-hydride batteries have demonstrated significantly lower electrochemical capacities due, in part, to kinetic limitations (e.g., see H. Yukawa, et al., Mater. Trans., 2000, 43, 2757-2762). Another significant challenge for and barrier to commercialization of V-based metal-hydride batteries is the degradation of the metal hydride electrode in the electrolyte (e.g., see Iwakura, et al. J. Electrochem. Soc., 2000, 147, 2503-2506), for example via oxidation and dissolution of vanadium from the electrode. As a result, conventional V-based metal hydride batteries have limited cycle stability, for example, losing a third of the capacity over 10 cycles.
In view of the above, there remains a need for V-based electrochemical systems, including V-based metal hydride batteries, which demonstrate improved stability and capacities. Provided herein are electrochemical systems, and associated methods, that address these, and other challenges.